I found the following solution: abstract class Addon { public string name = "0"; public void updateOfClassFields() { } }
class Users: Addon { override { public void updateOfClassFields() { name = "USERS"; } } } activated = [new Users, new Users]; activated[1].updateOfClassFields(); writeln(Core.activated[0].name ~ "\n" ~ Core.activated[1].name); out: 0 USERS